Freeze-dried coffee extracts for use as “instant coffee” are usually produced as granules, whereby aqueous coffee extract with a dry substance content of approximately 40% wt/vol. is foamed to a foam weight of approximately 450 to 750 g/l, the composition is cooled for approximately 30 minutes on freezing belts to a foam temperature of approximately −45° C. and the frozen product is ground at −40 to −50° C. The thus obtained granules are screened at low temperatures in order to eliminate the fines with grain sizes of less than 0.5 mm and particles with grain sizes above 3 mm. The quantity of fines, i.e., of particles with grain sizes below 0.5 mm, usually accounts for 30 to 35% wt. of the frozen total product. After screening, approximately 95% of the granules have grain sizes in the range from 0.5 to 3 mm, but often up to 5% of fines with grain sizes of 0.5 mm or less are still present. The proportion of particles between 0.5 mm and 1 mm is approximately 10 to 20% of the screened product. These granules are usually poured into trays and freeze-dried at operating pressures between 0.3 and 0.4 mbar (Capacitron values, corresponding to Thermotron values of approximately 0.4 to 0.6 mbar). The freeze-dried end-product normally has a bulk density of approximately 230 to 260 g/l.
A number of processes have been proposed in the prior art for producing “instant coffee” which readily dissolves in hot water and is commercially available as bulk powder contained in a sealed jar. While these have been successful, there has been a desire to improve such products. For example, there has been a need to provide “instant coffee” which can be conveniently dosed, and for which the strength of the resulting beverage can be easily controlled. Thus, the prior art has attempted to develop coffee tablets or cubes in an attempt to remedy these deficiencies.
Coffee tablets or cubes are generally prepared from soluble coffee extractives. This method involves subjecting ground coffee beans to the action of an extracting solvent and evaporating the concentrate abstract to the condition of an agglomerate, which is compressible into tablet form. Such coffee tablets and extraction procedures for preparing the same are described in U.S. Pat. No. 1,137,265 to Hubner and U.S. Pat. No. 3,121,635 to Eldred. These coffee tablets have not been commercially successful, most likely because they are subject to breakage due to their fragility and also because such tablets do not possess the same degree of aroma and flavor as other forms of powdered coffee. Further, low solubility is likely to result from strong compactation of the agglomerates. In this case the tablet strength may be very high but the solubility very low.
Canadian patents 964074 and 918494 teach that foaming or partly freezing of the coffee extract prior to the shaping of the coffee tablet can be used to give a more porous structure. It has however been found that this may result in a pore structure that is too open and that results in a less well defined shape. In addition to an unattractive appearance, tablets made according to these patents are also somewhat more susceptible to breakage and production of fines in the packages in which they are provided.
In an effort to reduce breakage and increase strength and ductility of the tables, it has been proposed to include binders in such tablets. For example, U.S. Pat. No. 1,951,357 to Hall describes a method of forming a compressed coffee tablet by incorporating with the coffee extract a liquid binder containing gelatin and dextrin. However, coffee tablets formed by these procedures have disadvantages in that the flavor of the pure coffee extractive is lost in the course of formulation since the extrinsic binder or vehicle is never completely removed from the beverage, and this loss contributes to the less desirable taste and appearance of the beverage. While it is possible to include a different binder material with the active ingredient to hold the tablets together, the use of conventional binders in coffee tablets is undesirable, because it results in a coffee beverage, rather than a pure coffee product, and the extraneous ingredients can adversely affect the taste characteristics of pure coffee.
U.S. Pat. No. 4,975,295 discloses a water-soluble coffee tablet made if a mixture of roast and ground coffee and an agglutinating agent. As the roast and ground coffee is not fully soluble in water, solids remain after the coffee is brewed. This requires a filter or other separation means to prevent the solids from appearing in the liquid coffee that is prepared from the tablet.
In addition, as noted above, known coffee tablets are hygroscopic and require special packaging in order to prevent moisture pickup. In addition, such tablets have a tendency to lose their aroma and flavor over time during storage. U.S. Pat. No. 4,975,295 does recognize this problem and suggests packaging the tablets in an impervious wrapping or a sealed enclosure. However, if the packaging is too tight around the tablet, this could lead to breakage. Thus, improvements over the products of this patent are desired.
Coffee is a beverage that has a taste and aroma which is can be found more desirable when the coffee beverage is fresh since the aroma may degrade over time and become “stale.” This is because the compounds which contribute flavor to the coffee are organic in nature and the flavor is the most desirable immediately after the coffee is brewed because the compounds which impart the flavor have not degraded. Over a period of time the organic compounds of the coffee oxidize by combining with oxygen in the water from which the coffee is brewed and the oxidation results in the degradation of the coffee and the loss of the desirable flavor. While conventional packaging is used in an attempt to control this, it may still remains as a problem.
Accordingly, there is a need for a coffee tablet that has a good appearance, is sufficiently strong and ductile to resist breakage and is capable of retaining its flavor and taste during storage. The present invention aims to provide such tablets. A further aim is to provide a coffee tablet with an acceptable solubility.